1. Field of the Invention
The present invention relates to a driving device for electromagnetically driving an object to be driven, and an optical apparatus and an image pickup apparatus which are equipped with the driving device.
2. Description of the Related Art
A lens driving device for cameras has conventionally been proposed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. H11-190815, in which a small cylindrical stepping motor is disposed parallel with a lens, and the stepping motor drives the lens by means of a lead screw or the like.
Further, a lens driving device using a voice coil actuator has been disclosed e.g. in Japanese Laid-Open Patent Publication No. H04-093807. The voice coil actuator is provided with one of a magnet and a coil fixed to a support frame that supports a lens group, and the other to a lens barrel, to thereby drive a zoom lens. In this voice coil actuator, the coil is one-phase controlled, and electric current is applied to the coil in the normal direction or in the reverse direction while detecting the position of the lens by a position sensor. In this way, the lens is positioned in a desired position.
In the former driving device, however, noise is generated by sliding contact between a member held in mesh with the lead screw to function as a female thread and the surface of the lead screw, and hence when the driving device is used e.g. in a video camera, the sliding noise can be recorded as untoward noise. Further, if the lead screw is deformed, the deformation can be transmitted to the member serving as the female thread to cause the member to displace the lens in a direction orthogonal to the optical axis resulting in degraded accuracy in lens positioning.
Furthermore, when the former driving device is used for driving the zoom lens of a video camera, the driving speed at which the zoom lens is driven is slow, and hence it takes time to drive the zoom lens to a position where a desired focal length is obtained, which results in degraded quick shooting performance.
The latter driving device, i.e. the driving device using a voice coil actuator, is superior to the former driving device in zoom speed, quietness, and accuracy in lens positioning. However, in this driving device, the friction coefficients of drive guide parts vary due to changes in the operating environment and aging. Further, when shooting is performed in an unexpected shooting posture, the lens cannot be positioned accurately.
Moreover, when the camera is used in an unexpected shooting posture, the lens cannot be accurately controlled to a desired position, and in worst cases suffers from vibration, which hinders the lens from being stopped at a correct position.